Field of the Disclosure
The present disclosure relates generally to power converters, and more specifically, to ac-dc and/or dc-dc switched mode power converters that use a power factor correction (PFC) stage.
Background
Many electrical devices, such as cell phones, personal digital assistants (PDA's), laptops, etc., use power to operate. Because power is generally delivered through a wall socket as high voltage alternating current (ac), power converters are typically used to convert alternating current (“ac”) power provided by an electrical outlet into direct current (“dc”) to supply an electrical device or load.
Many power converters employ a power factor correction (PFC) stage in order to correct the non-sinusoidal wave shape of the current drawn from the ac source by the power converter. If the input ac current and voltage waveforms are sinusoidal and perfectly in phase, the power factor of the power converter is 1. In many parts of the world, legislative requirements for power converter manufacturers to ensure that power converters have power factors greater than 0.9. In high voltage applications the power converters typically have output power ratings of 75 Watts or more. Safety agencies generally require inclusion of PFC stages with converters with output power ratings of 75 Watts or higher.
There are generally two types of PFC stages that may be used with a power converter, namely a passive PFC circuit and an active PFC circuit. A passive PFC stage typically comprises of passive devices such as resistors, capacitors, and inductors. An active PFC circuit typically comprises of a combination of passive and active devices such as capacitors, inductors, and MOSFETS. More specifically, active PFC stages include buck converters, boost converters, or buck-boost converters. In high power applications, common methods to increase the power factor of a power converter include using an active PFC stage.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.